Such a rubber cartridge spring is disclosed in Published European Application (EP-A) 0009120. The sealing rings made of rubber are disposed in this case about the outer circumference of the window tube and are provided with a certain oversize with respect to the inside diameter of the outer tube to assure the contact pressure necessary for the achievement of a seal. The amount of the oversize is, however, limited by the necessity of displacing the window tube axially in the outer tube during assembly. The reason for this limitation is that the displacement involves a considerable abrasive stress on the surface of the rings and a corresponding shear stress on the body of material forming the sealing rings. Even if established production tolerances are precisely observed, therefore, the percentage of leaky, that is, faulty rubber cartridge springs is relatively high.